Process for producing a plastic composition for battery boxes



Patented July 4, 1950 Cecil B. Wilde, Comptom Calif assignor to--' Staufier Chemical Company; a corpor-ationof California N Drawing. Application "July 6, '1948,

Serial No. 37309 3 Claims. (01. ioe ozi This invention relates to plastic compositions and particularly to those which are'impervious to water, resistant 'to the'action of sulfuric acid of the strength'usually employed in storage batteries and which, when molded, are capableof retaining their character under ordinary thermal conditions. I

It is well known that, in the fabrication'ofbattery boxes and like articles which, in use, are subjected tothe action of sulfuric acid and which are required to have both mechanical and dielectric strength, it is necessary to ultilize materials which are 'at least partially unafiected by the acid. A typical composition as used heretofore has consisted of a mixture'of a suitable hydrocarbon such as asphalt or other bitumen, a filler such as diatomaceous earth or'the" like, and asbestos fibres. This material has been prepared by first melting the hydrocarbon and placing it in a mixer together with the fibrousm'aterial and the filling material. Because of the necessity of employing a hydrocarbon material which has inherently a relatively high softening point, the mixing of the hydrocarbon and fibrous material must be at a relatively hightemperature. To secure adequate mixing, the mixing operation must be continued for a relatively long period of time. As a consequence, the fibresb'ecome broken and the tensile strength of the ultimate product is affected adversely; if a vegetable fibre is employed, it is scorched, charred or at least lowered materially in strength. Further, it is diflicult to distribute the fibrous material through the sticky, plastic mass of hydrocarbon and, as a consequence, the mixing must'be'continued for an inordinately long period of time or else the mixture is not homogeneous. In either case, the properties of the substance are afiected adversely with respect to such characteristics as tensile strength, dielectric strength, acid resistance and uniformity. Such a process as I have described is disclosed in Patent It has also been proposed in Patent 1,892,703

to mix the three constituents in the dry state and then apply heat. This process provides some improvement over that previously described. However, while the dry mix may be homogeneous, this is not always true of themass after heating, for apparently the hydrocarbon does not bondto the fibrous filler when the'heat is applied and the fibres are not impregnated to the desired extent. Increasing the-degrees of heating merely scorches the fibre.

In accordance With the present invention, I prepare each of-the constituents of the mixture separately; grinding the-hydrocarbon material tofin'ely divided form, for example, so that at 1east'80%'of the hydrocarbon will pass a 40 mesh screen; the fibrous material, which has been previously placed in shredded form while dry, is fiuffedso that the'material is of relatively low density. The filler is also 'in finely divided form, for example, sothat all of it will pass a 100 mesh screen. The hydrocarbon material usually comprises from 45% to of the mixture and the earth from 25% to 45%. The three constituents are then mixed'ina suitable mixing device, such as a paddle mixer, to form a homogeneous mass of the three. Thus, the hydrocarbon material is fairly distributed throughout the fibrous material and the earth, and the fibres are uniformly coated with the earth and hydrocarbon material without destroying-the individual fibres or reducing their'length. During the course of the mixing operation, about 10% by weight of water is added tothe mixture undergoing mixing. This facilitatesdeposit of the finely divided earthand hydrocarbon on the fibres. The quantity of water added should be between 5% and 20% by weight of the mass; this quantity of water is-insuificient to make the mass wet or soggy; infact, a visual; examination of the material issuing from the mixer will fail to reveal the presence of the waterand the mixture can be squeezed or pressed in the hand without obtainingany evidence of the presence of water.

ployed, the fibre is protected against burning or scorching or lowering of the fibre strength. Due

. are relatively expensive.

cotton, such as kraft, sulfite to the pressure exerted upon the mixture in the length. The material is then preferably exposed to the atmosphere for a period of from 1 to 4 minutes to permit the mass to steam freely; durmg the free steaming period, the mass is subject to additional heating by means of radiant 1 heaters disposed closely adjacent to the mass of material; a convenient manner of obtaining this is to move the stream of material issuing from the masticator extruder along on' a conveyor beneath suitable radiant heaters. This permits any excess water vapor present as steam to issue from the material. The. material is then again preferably kneaded in a second masticator for;

a short period of time to provide further uniformity in the mixture. ready for processing in the usual manner in a suitable press to form a battery box or like 1 article.

The usual fibres employed heretofore have generally been asbestos or cotton linters; both I have found that I can utilize other vegetable fibres alone or mixed together in place of cotton or in addition to or like fibres. These are used in an amount up to about 20% of the mixture and preferably 10%-12% by weight of the mixture. The use of such fibres is made possible because of the absence of high temperature conditions and long mixing periods which either destroy the fibre length or reduce its strength objectionably, or both.

Emample 1 As illustrative of the practice of the present invention, 52 parts of an asphalt having a ball and ring softening point of 275 F. and a penetration of 13 115 F. and ground to minus 40 mesh were mixed with 11 parts of kraft pulp obtained by shredding used kraft paper bags together with 37 parts of diatomaceous earth, all

minus 100 mesh, The three materials were uniformly mixed in a dry mixer, 5%-20% by weight of the mixture of water being added during the 1 course of the mixing operation. The mixture was then passed to a masticator extruder to a temperature of 250-325 F., wherein the ma' terial was heated until the asphalt had melted and uniformly impregnated the earth and fibre. The mixture was then permitted to steam freely while heated by radiant heat for two minutes, so that no loss of temperature occurred. After this, it was kneaded for two to four minutes when it was ready for formation into a typical battery box in a press and in the well known manner.

The composition, when molded in this manner had the following characteristics:

The procedure outlined under Example 1 was followed, but equal parts by weight of cotton The material is then 4 linters and shredded kraft pulp were employed instead of the kraft pulp. The battery box had the following characteristics:

Tensile strength 1443 pounds per square in. Percent elongation 1.96% Impact strength .50 foot pound Bulge test:

Side 0.063 inch End 0.150 inch Example 3 The procedure outlined under Example 1 was followed utilizing 12% of dry, fluffed, shredded sulfite pulp. The battery box which was formed was of acceptable characteristics and properties.

Example 4 The procedure outlined under Example 1 was followed, but equal parts by weight of cotton linters and shredded sulfite pulp were employed. The battery box which was formed was of acceptable characteristics and properties.

Example 5 The'procedure outlined under Example 1 was followed, but equal parts by weight of cotton linters, shredded sulfite pulp, and shredded kraft pulp were employed. The battery box which was formed was of acceptable characteristics and properties.

Iclaim:

1; A process for producing a plastic composition for battery boxes comprising mixing together in a dry state and substantially at a normal atmospheric temperature a bitumen in the form of. a dry, finely divided solid, a finely divided earth, and a pre-fiuffed dry fibrous material of low density and selected from the group consisting of kraft pulp, sulfite pulp and mixtures thereof with cotton linters, the mixture containing from 45% to 55% of the bitumen, from 25% to 45% of the earth, and from 10% to 20% of the fibrous material, adding to the mixture during the mixing from 5% to 20% of water and continuing the mixing until a dry homogeneous mixture is formed, and thereafter heating the mixture to a temperature of from 250 F. to 325 F. while kneading the material under pressure until the bitumen is melted in the mixture and the mixture is substantially free of water.

2. A process for producing a plastic composition for battery boxes comprising mixing together a dry finely divided bitumen, a finely divided earth, and a dry fibrous pre-fluifed ma terial selected from the group consisting of kraft pulp, sulfite pulp and mixtures thereof with cotton linters, the mixture containing from 45% to 55% of the bitumen, from 25% to 45% of the earth, and from 10% to 20% of the fibrous material, the mixing being at a temperature whereat the bitumen is a solid, adding to the mixture during the mixing from 5% to 20% of water and continuing the mixing until a dry homogeneous mixture is formed, and then heating the mixture to a temperature of from 250 F. to 325 F. while kneading the material under pressure until the bitumen is melted in the mixture and the mixture is substantially free of water.

3. A process for producing a plastic composition for battery boxes comprising mixing together a, dry finely divided solid bitumen of which at least will pass a 40 mesh screen, a

finely divided earth, and a dry pre-fluffed fibrous material selected from the group consisting of kraft pulp, sulfite pulp and mixtures thereof with cotton linters, the mixture containing from 45% to 55% of the bitumen, from 25% to 45% of the earth, and from 10% to 20% of the fibrous material, adding to the mixture during the mixing from 5% to 20% of water and continuing the mixing until a dry homogeneous mixture is formed, and then heating the mixture to a temperature of from 250 F. to 325 F. While kneading the material under pressure until the bitumen is melted in the mixture and the mixture is dry.

CEC'IL B. WILDE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 337,472 Allen Mar. 9, 1886 1,156,122 Woodley Oct. 12, 1915 1,751,690 Faben Mar. 25, 1930 1,771,643 Lukens July 29, 1930 1,892,703 Lindh Jan. 3, 1933 2,023,675 Fischer Dec. 10, 1935 

1. A PROCESS FOR PRODUCING A PLASTIC COMPOSITION FOR BATTERY BOXES COMPRISING MIXING TOGETHER IN A DRY STATE AND SUBSTANTIALLY AT A NORMAL ATMOSPHERIC TEMPERATURE A BITUMEN IN THE FORM OF A DRY, FINELY DIVIDED SOLID, A FINELY DIVIDED EARTH, AND A PRE-FLUFFED DRY FIBROUS MATERIAL OF LOW DENSITY AND SELECTED FROM THE GROUP CONSISTING OF KRAFT PULP, SULFITE PULP AND MIXTURES THEREOF WITH COTTON LINTERS, THE MIXTURE CONTAINING FROM 45% TO 55% OF THE BITUMEN, FROM 25% TO 45% OF THE EARTH, AND FROM 10% TO 20% OF THE FIBROUS MATERIAL, ADDING TO THE MIXTURE DURING THE MIXING FROM 5% TO 20% OF WATER AND CONTINUING THE MIXING UNTIL A DRY HOMOGENEOUS MIXTURE IS FORMED, AND THEREAFTER HEATING THE MIXTURE OF A TEMPERATURE OF FROM 250*F. TO 325*F. WHILE KNEADING THE MATERIAL UNDER PRESSURE UNTIL THE BITUMEN IS MELTED IN THE MIXTURE AND THE MIXLTURE IS SUBSTANTIALLY FREE OF WATER. 